Hydrocarbon conversion processes in which a hydrocarbon or mixture of hydrocarbons and steam or a hydrocarbon and one or more of hydrogen, carbon monoxide and carbon dioxide are well known processes that are conducted at high temperatures and pressures in apparatus typically made of steels containing one or more of Ni and Co. Carburization of system metallurgy and metal dusting, are problems encountered with using such steels.
In general, metal dusting of steels is experienced at temperatures in the range of 300° C. to 900° C. in carbon supersaturated (carbon activity>1) environments having relatively low (about 10−10 to about 10−20 atmospheres) oxygen partial pressures. Basically rapid carbon transfer to the steel leads to “metal dusting”, a release of particles of the bulk metal.
Methodologies available in the literature to control metal dusting corrosion involve the use of surface coatings and gaseous inhibitors, especially H2S. Coatings can degrade by inter diffusion of the coating constituents into the alloy substrate. Thus they tend to be suitable for short term protection but generally are not advisable for long term protection, especially for twenty or more years.
Corrosion inhibitors using H2S has two main disadvantages. One is that H2S tends to poison most catalysts used in hydrocarbon conversion processes. Another is that H2S needs to be removed from the exit process stream which can be expensive.
An object of the present invention is to provide improvements in reducing metal dusting corrosion.
Another object is to provide materials that are resistant to metal dusting corrosion in petrochemical processes where carbon supersaturated and low oxygen partial pressure environments are present.